Home FOC Calculator
Arrow FOC Calculator
Calculate your arrow's Front of Center (FOC) balance.
Optimize for hunting penetration or target accuracy.
Works for all arrow types and setups.
Quick navigation: Calculator · Why Calculators Differ · FOC Charts · How to Measure · FAQs
💡 Easton recommends 10-15% FOC for hunting; its target guidance is generally 7-15% indoors and 10-15% outdoors.
If you change point or insert weight to adjust FOC, re-check arrow spine before shooting.
How to calculate arrow FOC — formula and example
Easton's FOC method uses the complete arrow, the arrow length from the throat of the nock to the end of the shaft, and the measured balance point from the throat of the nock.
| Measurement | Value |
|---|---|
| Arrow length (L) | 29 inches |
| Balance point (A) | 17.5 inches from nock throat |
| Center of arrow (L ÷ 2) | 14.5 inches |
| Distance ahead of center | 3.0 inches |
| FOC percentage | 10.3% |
Formula: FOC% = [(A − L/2) ÷ L] × 100
FOC% = [(17.5 − 14.5) ÷ 29] × 100 = 10.3%
A 10.3% result falls within Easton's 10-15% hunting recommendation and its 10-15% outdoor-target guidance.
🎯 Calculated your FOC? Complete your arrow optimization:
Next: Arrow Weight Calculator — verify adequate total
weight.
Then: Kinetic Energy Calculator — confirm penetration
power.
Adjust: Use the Arrow Insert Weight Calculator to
find the exact insert weight needed to hit your FOC target.
Tune: Tie your D loop — then paper tune to confirm arrow flight with your final build.
Understanding Front of Center (FOC)
What is FOC?
FOC (Front of Center) describes how far the finished arrow's balance point sits in front of its physical midpoint, expressed as a percentage of arrow length. More mass in the point, insert, or other front components generally moves the balance point forward; more rear mass generally moves it back.
FOC% = [(Balance Point − Arrow Length ÷ 2) ÷ Arrow Length] × 100
What FOC changes
Easton explains that higher FOC generally promotes stable flight but can make the arrow shed trajectory more quickly, while very low FOC can hold a flatter trajectory yet become less stable. FOC is therefore a tuning and balance variable, not a stand-alone penetration score.
FOC vs. total arrow weight
FOC tells you where the arrow's mass is distributed. Total arrow weight tells you how much mass the finished arrow has. Both affect the complete system, along with spine, broadhead or point design, tuning, speed, and shot execution.
Use our arrow weight calculator for finished mass and the arrow spine calculator after changing front-end weight.
Why measured FOC can differ from component-weight estimates
Easton's published FOC formula is based on two direct measurements: finished arrow length and the balance point of the complete arrow. If those two measurements are the same, the formula produces the same result.
Component-weight calculators can differ because they must model where each component's mass sits along the arrow. Catalog weights, wraps, collars, bushings, vane position, adhesive, and rounding can all shift an estimated balance point.
For that reason, the component mode on this page is labeled as an estimate. For a finished arrow, physically balance the complete arrow and enter the measured balance point above.
FOC recommendations by discipline
Target archery
Easton's current guidance says a general FOC range of 7-15% indoors and 10-15% outdoors can provide stable flight, useful momentum, and accurate trajectory. Lower values may still work for some indoor setups; the exact optimum depends on the complete arrow and bow.
Bowhunting
Easton recommends 10-15% FOC for hunting setups, particularly when stability and accuracy at longer distances matter. That is a useful manufacturer-backed starting range, not a guarantee of penetration or hunting performance.
What about FOC above 15%?
Higher FOC is not automatically wrong, but Easton notes that greatly exceeding its common target ranges can increase vertical dispersion at longer distances. It also cautions that FOC above about 20% can make finger release consistency more critical. If you intentionally build a high-FOC arrow, confirm trajectory, spine, broadhead flight, and grouping with your actual equipment.
FOC quick reference chart
| FOC Range | How to interpret it |
|---|---|
| Below 7% | Below Easton's general indoor-target range; verify stability and tuning. |
| 7-10% | Within Easton's general indoor-target guidance, but below its 10-15% hunting/outdoor-target range. |
| 10-15% | Easton's recommended hunting range and general outdoor-target range. |
| 15-20% | Above Easton's common recommendation; test trajectory, grouping, and tuning with the finished setup. |
| 20%+ | Very high FOC. Easton cautions that excessive FOC can increase long-range dispersion and release sensitivity. |
Use these ranges as references, not game-size prescriptions. FOC is one part of the complete arrow system.
How to increase or decrease FOC
🎯 Add front weight
Increases FOC: Heavier points, inserts, collars, or other front components generally move the balance point forward.
🪶 Reduce rear weight
Increases FOC: Lighter nocks, vanes, or wraps can move the finished balance point forward.
⚖️ Reduce front weight
Decreases FOC: A lighter point or insert generally moves the balance point rearward.
📏 Re-measure after changes
Do not assume a fixed percentage change per 25 grains. Build the arrow, balance it again, and calculate the new measured FOC.
Front-weight changes also affect dynamic spine. After changing point, insert, collar, or outsert mass, cross-check the setup with the Arrow Spine Calculator and the shaft manufacturer's current selector.
How to measure your arrow's balance point
Equipment needed
- Complete finished arrow with the components you actually shoot
- Ruler or measuring tape
- Pencil or removable marker
- A narrow balance edge
Step-by-step instructions
1. Complete the arrow: Install the point or broadhead, insert/outsert, nock, vanes, wraps, and other components that will be on the arrow when shot.
2. Find the balance point: Rest the arrow on a narrow edge and slide it until it balances level.
3. Mark the balance point: Mark that location on the shaft.
4. Measure balance point distance: Measure from the throat of the nock to the balance-point mark.
5. Measure arrow length: Measure from the throat of the nock to the end of the shaft, excluding the point, as specified by Easton's FOC method.
6. Calculate FOC: Enter both measurements in the calculator above.
Technical sources
FOC calculator FAQs
What is FOC in archery?
FOC (Front of Center) is the percentage by which a finished arrow's balance point sits in front of the arrow's physical midpoint. It describes weight distribution, not total arrow weight. Easton's formula uses arrow length from the throat of the nock to the end of the shaft and the measured finished-arrow balance point.
What FOC does Easton recommend for hunting arrows?
Easton recommends 10-15% FOC for hunting setups. Treat that as a manufacturer-backed starting range and then verify spine, tuning, broadhead flight, trajectory, and grouping with the finished arrow.
What FOC is used for target archery?
Easton's current guidance gives a general range of 7-15% for indoor target archery and 10-15% for outdoor target archery. The best value for a specific setup still depends on the complete arrow, bow, tune, and shooting discipline.
How do I measure my arrow's balance point?
Balance the complete finished arrow on a narrow edge and mark the point where it sits level. Measure from the throat of the nock to that balance-point mark. Also measure arrow length from the throat of the nock to the end of the shaft, excluding the point.
Can FOC be too high?
Yes. Easton notes that greatly exceeding its common FOC range can increase vertical dispersion at longer distances, and that FOC above about 20% can make finger-release consistency more critical. High FOC should be tested with the actual bow and arrow rather than assumed to be automatically better.
How do I increase my arrow's FOC?
Adding mass toward the front or reducing mass toward the rear generally increases FOC. There is no universal rule that a fixed number of grains changes FOC by a fixed percentage, so re-balance and re-measure the finished arrow after changes. Re-check spine as front-end mass changes.
Why does the component-weight estimate differ from my measured FOC?
The component mode estimates where component mass sits along the arrow. The real arrow can also contain wraps, collars, bushings, adhesive, and different vane positions. For a finished arrow, the physically measured balance point is the better input.
Does switching points or broadheads change FOC?
It changes FOC if the replacement changes the arrow's mass distribution. A broadhead and field point with the same total mass may produce little change, while a heavier or lighter front component can move the balance point. Re-measure the finished arrow whenever the build changes.